Write five characteristic features of Phylum Cnidaria?

Explanation

Characteristic features of phylum cnidaria:
1. Cnidarians, are aquatic, sessile or free swimming, solitary or colonial forms with radial symmetry except for sea anemones.
2. The name Cnidaria is derived from cnidocytes or cnidoblasts with stinging cells or nematocyst on tentacles. Cnidoblasts are used for anchorage, defense, and to capture the prey.
3. Cnidarians are the first group of animals to exhibit tissue level organisation and are diploblastic.
4. They have a central vascular cavity or coelenteron (serves both digestion and circulatory function) with a single opening called mouth or hypostome, which serves the process of ingestion and egestion.
5. Digestion is both extracellular and intracellular.
6. The nervous system is primitive and is formed of diffused nerve net.
7. Cnidarians like corals have a skeleton made up of calcium carbonate.
8. Cnidarians exhibit two basic body forms, polyp and medusa. The polyp forms are sessile and cylindrical (Eg: Hydra, Adamsia), whereas the medusa are umbrella shaped and free swimming.
9. Cnidarians which exist in both forms, also exhibit alternation of generations in their life cycle (Metagenesis).
10. Development is indirect and includes a free swimming ciliated planula Jarva. Eg: Physalia (Portugese man of war), Adamsia (sea anemone).